1. Field of the Invention
The present invention relates to a gas sensor having a gas sensor element for detecting the concentration of a particular gas.
2. Description of the Related Art
A gas sensor is mounted onto an intake system (e.g., an intake pipe or an intake manifold) or an exhaust system of an internal combustion engine, such as a diesel engine or a gasoline engine, for controlling, for example, combustion conditions by monitoring the concentration of a particular gas. A gas sensor generally used for performing such control is fixed by providing an externally threaded portion on the outside of a case (metallic shell) adapted to accommodate a gas sensor element therein, and is threadingly engaged with an internally threaded portion provided in a wall of the intake or exhaust system.
Meanwhile, in order to improve safety in the event of collision of a vehicle having an internal combustion engine, a clearance must be provided between the hood and engine parts; thus, the length of outward projection of the gas sensor from the intake system must be shortened. However, the gas sensor mentioned above has a limitation in shortening the length of outward projection of the gas sensor from the intake system. This is because connection terminals and lead wires for leading out detection outputs from the gas sensor element are extended rearward from the gas sensor.
Under these circumstances, a so-called lateral-lead-out-type gas sensor is known, as described in Patent Document 1, having a connector portion which extends, in a direction intersecting the axial direction, from a separator disposed on the rear side of the gas sensor element and to which detection outputs from the gas sensor element are led. According to this gas sensor, the axial height of the gas sensor is lowered, thereby shortening the length of projection of the gas sensor from the intake system when mounted to the intake system.
[Patent Document 1] Japanese Patent Application Laid-Open (kokai) No. 2011-145270
3. Problems to be Solved by the Invention
The lateral-lead-out-type gas sensor described in Patent Document 1 has a separator equipped with connection terminals disposed on the rear side of the gas sensor element, and allows for detection outputs to be led out from the connection terminals. A laterally extending lead frame is welded to the rear ends of the connection terminals; furthermore, the lead frame is welded to connector terminals extending from the connector portion. Thus, the lateral-lead-out gas sensor gives rise to problems of deterioration in production efficiency resulting from an increase in the number of welds, and an increase in the number of components resulting from use of the lead frame. Meanwhile, since the gas sensor element assumes a high temperature as a result of heating by its own heater and exposure to, for example, exhaust gas, the connection terminals connected to the gas sensor element are preferably formed of a heat resisting metal. By contrast, since the connector terminals are required to have low internal resistance for high electrical conductivity, generally, the connector terminals are preferably formed of a copper-based material. In the case where the materials of the connection terminals and the connector terminals differ, difficulty may be encountered in welding these terminals.